Abstract: Objective To investigate the effects of exercise intensity on myocardial fibrosis in diabetes rats. Methods High-fat diet and low-dose streptozotocin were used to induce type 2 diabetes mellitus(T2DM) rats. Five groups of Sprague-Dawley rats were studied: non-T2DM (normal, N); T2DM(DM);T2DM+low-intensity swimming (DM+LM); T2DM +moderate-intensity swimming (DM+MM); T2DM +high-intensity swimming (DM+HM).The blood pressure was measured by carotid artery intubation. HE, Masson and immunohistochemical staining were used to observe pathology characteristics of hearts. Results Body weight, fasting blood glucose and blood pressure were significantly higher in the diabetic groups than the normal groups and only moderate intensity exercise normalized it in diabetic rats ( P＜0.05). T2DM induced myocardial remodeling and cardiac fibrosis in rats as illustrated by irregular collagen structure network in the interstitial and perivascular area of cardiac muscles which were reversed by moderate intensity exercise ( P＜0.05). Conclusion Moderate intensity exercise can reduce cardiac fibrosis in diabetes rats